A prior art yarn supply system for a flat knitting machine comprises a yarn spool, a yarn tensioning unit comprising a yarn storing and feeding device to which a yarn can be supplied from the yarn spool for an intermediate store of the yarn on a storage drum of the feeding device. The yarn can be actually withdrawn from said storage drum through a yarn tensioning device arranged at the withdrawal end of the storage drum. The yarn withdrawn from the storage drum of the yarn feeding device is fed to a yarn take-up arm which is pivotally journalled under a spring-load and which is adapted for intermittently taking up an excess of yarn in case the yarn tension drops below a predetermined yarn tension value.
A flat knitting machine comprises a stationary needle bed and a carriage which can be reciprocated with respect to said needle bed for operating the needles and for moving a thread feeder arranged at the carriage along the needle bed so as to supply the yarn to the respective operated needles. The movement of the carriage of a flat knitting machine does not terminate at the respective ends of the needle bed of the knitting machine, but there is a so-called over-movement of the carriage with respect to the needle bed of the flat knitting machine. This over-movement of the carriage at both end positions of its horizontal movement over the needle bed is carried out when changing the thread feeder arranged at the carriage during the colour change as well when only changing the direction of the movement of the carriage when further working by means of the same thread feeder without changing the colour. The yarn consumption of the knitting machine during the normal operation when the carriage is within the normal working area, i.e., between the respective ends of the needle bed, is essentially constant. The yarn consumption drops at the respective remote ends, i.e., during the over-movement of the carriage. Hence, a surplus of yarn is to be taken back in a controlled manner at the respective remote ends of the fabric so as to make the edges of the knitted fabric look satisfactory.
In the prior art yarn supply system, the spring-loaded arm intermittently takes up the surplus or excess of yarn by a pivot movement.
The spring-loaded arm has the tendency to cause vibrations and oscillations in the yarn tension which in turn negatively affects the continuity in building up the respective stitches and thus results in an unsufficient knitting quality.
In view of this state of art, the present invention s based on the technical task of how to further develop a yarn supply system for a flat knitting machine adapted for manufacturing a high quality knitted fabric having an essentially constant stitch size.
This technical task is solved by a yarn supply system in accordance with the prior art portion of claim 1 having the features indicated in the characterising portion thereof.
In accordance with the present invention, the operation of the yarn take-up means is inhibited in response to predetermined operating conditions of the flat knitting machine. These operating conditions may be the relative position of the carriage with respect to the needle bed and/or the actual movement of the yarn withdrawn from the yarn tensioning unit.
Preferably, the operation of the yarn take-up means is inhibited during the so-called "normal" operation of the flat knitting machine, i.e., during the movement of the carriage between the respective ends of the needle bed. Hence, the occurrence of any oscillations of the yarn take-up means during the normal knitting operation is prevented. In other words, slight oscillations may only occur at the very short operating time during the over-movement of the carriage. As a result therefrom, the knitted fabric manufactured by a flat knitting machine having a yarn supply system in accordance with the present invention has a very constant stitch size and thus a high quality.
Advantageous embodiments in accordance with the present invention are defined in the subclaims.